The invention relates generally to the application of coatings to webs, for example the application of paint to metal roll stock. If paint (or some other coating) is to be applied to metal roll stock, a typical way to do this is by means of a production line that starts at one end with metal roll stock that is desired to be coated, continues to a coater which applies the paint, proceeds to a drying or curing area, and ends with metal roll stock that has been coated. Such production lines are well known.
Prior-art coating production lines, however, have had many problems. One problem is that it is all too easy to apply a coating that is too thin or too thick. If the coating is thicker than necessary, money is wasted because too much coating gets used. Another problem is that with many coaters, there can be unevenness in the coating, with puckering, gapping, voids, and the like. Still another problem is that with many coaters, there are wear items that wear out quickly. When a wear item wears out, this forces the production line to be shut down. Finally, the need to make a change in the coating fluid (e.g. a change in paint color) may also require shutting down the production line.
As set forth in parent U.S. Pat. No. 6,656,529, a coater may employ a nozzle. The nozzle is elongated and is oriented with its elongated dimension perpendicular to the direction of motion of the web that is being coated. Coating (for example paint) is present in the nozzle and is able to flow out the nozzle toward the web. The nozzle will thus define a leading edge (which the web or applicator roll encounters first along its direction of travel) and a trailing edge (which the web or applicator roll encounters later along its direction of travel). The leading edge, the trailing edge, and the web or roll itself help to define where the paint goes and where it does not go. Clever selection of geometry and materials in the leading and trailing edges, as discussed in parent U.S. Pat. No. 6,656,529, permit the nozzle to serve its purpose effectively.
A moment's reflection will prompt a realization that even with ideally selected materials and geometry for the leading and trailing edges of the nozzle, a nontrivial design problem remains. How are the ends of the nozzle to be designed? One end will be at or near one edge of the web that is to be coated, while the other end will be at or near the other edge of the web that is to be coated. If little or no thought is given to the designs of the two ends of the elongated nozzle, then coating (e.g. paint) is likely to leak out the ends, and indeed may spray out depending on the pressure in the nozzle.
In the case where a transfer roll is used to transfer coating from the nozzle to the web, any excessive amount of coating leaking out the ends is likely to “sling” out due to centrifugal force, traveling in uncontrolled directions. On the other hand if the nozzle is applying coating directly to a web, then any leaking excess coating will lead to unevenness and possibly excess material along the edges of the web.
Enormous amounts of time and energy have been devoted by many investigators to attempt to address the problem of what to do with ends of such applicator nozzles. One approach is to try to devise “end seals,” one at each end of the nozzle, which are intended to seal to the web or applicator roll, so as to block leakage out the ends of the nozzle. Unfortunately, many end seal designs that have been proposed have not served their purpose well. Some end seal designs are wear items, wearing out often and requiring replacement. Other end seal designs will “plunge” into the flexible surface of an applicator roll and will cause the applicator roll to wear and to lose surface material due to the wear. Still other end seal designs are extremely sensitive to even the smallest changes in spacing and geometry as between the nozzle and the web or applicator roll; with some end seal designs even a small change can lead to excessive wear on the one hand or excessive leakage on the other hand.
There is thus a great need for end seal designs that do not wear out too fast, that do not damage an applicator roll, and that are not unduly sensitive to changes in spacing and geometry as between the nozzle and the web or applicator roll surface. It has proven to be important to develop end seals that permit deep plunge into the application surface without overloading the end seal or damaging the application surface.
Yet another problem in the design of coaters is that it is desired to have close control over the manner in which the nozzle applies the coating to the surface being coated (e.g. the web or applicator roll). In past designs it is commonplace to try to achieve this control by moving the nozzle closer to or further from the surface being coated. Close control of such a distance is not easy, because of manufacturing tolerances, wear and expansion of transfer rollers, and other factors. Even if one is able to control such a distance closely, this does not control, as closely as one might wish, the manner in which the coating is applied to the surface being coated.
There is thus a great need for a coater design that permits more subtle control over the manner in which the nozzle applies the coating to the surface being coated. Such a design needs to work well with whatever end-seal design is to be employed.